A preferred field of application is the preparation of samples for microstructure diagnostics by transmission electron microscopy (TEM). Samples suitable for microstructure diagnostics by transmission electron microscopy are also referred to as TEM samples.
Techniques which are as accurate, low in artefacts, reliable and quick as possible are sought after for the preparation of samples for microstructure diagnostics. TEM samples require a sample portion with a relatively thin, electron-transparent examination region, i.e., an examination region through which an electron beam is able to pass. The target region to be examined should lie in this electron-transparent examination region. The target region is that spatially restricted region of interest to the examination.
In principle, thinning in a purely mechanical manner with relatively few artefacts is possible, particularly in ceramics and semiconductors, but this requires much technical skill to lead to a reproducible sample quality, at least to some extent. Moreover, there already are a multiplicity of, in part, very complicated techniques for producing sufficiently thin, electron-transparent regions on TEM samples. In particular, they include mechanical pre-thinning (grinding, polishing, cavity grinding), followed by an ion beam etching process, the cutting out of thin sections using a focused ion beam (FIB) and ultramicrotomy.
Methods for TEM sample preparation operating with a combination of laser beam processing and ion beam processing have also already been proposed. By way of example, DE 10 2004 001 173 B4 describes a method of preparing TEM samples, in which material is ablated from a substrate of a sample material by ultrashort pulse laser ablation in a vacuum chamber such that a narrow web remains, the latter subsequently being bombarded at a flat angle by noble gas ions such that an electron-transparent region arises in the region of the web.
Currently, the assumption is made that the laser-based sample preparation may only be a first step for preparation of TEM samples due to the non-negligible laser influence layer, and the first step should be followed by a less damaging second step in which the electron beam transparency is established. The second step is typically carried out using a focused ion beam (FIB) or a broad ion beam (BIB).
Processing by a focused ion beam (FIB processing) and the broad beam processing (BIB processing) differs, inter alia, in respect of the arising costs. While a broad ion beam etching installation is commercially available for moderate procurement costs, barely raises follow-up costs apart from electricity and etching gas and maintenance costs and may be operated without problems by technical staff, the procurement of an installation for FIB processing is reflected in the budget by much higher procurement costs, the installation being substantially more expensive in terms of maintenance and requiring an operator with significantly better training than a broad ion beam etching device.
Moreover, there is a clear difference in terms of the accessible geometry between samples produced by FIB and broad ion beam preparations. As a result of the relatively low dose, the overall volume ablation rates of FIB beams are significantly lower than those of broad ion beam installations. As a result, practical limits are placed on the FIB technology in respect of the accessible sample dimensions—these days, typical FIB lamellas for the examination by TEM have dimensions of, e.g., 20×5×0.5 μm3.
On the other hand, examination of large-area TEM preparations is becoming ever more important. This is true, for example, in view of the TEM examination of 3-D integrated microelectronic components. Attempts are made to prepare a relatively large area, thin sample portion from a sample body by material-ablating processing, e.g., by laser beam processing, and to subsequently produce an electron-transparent examination region, comprising a target region to be examined, in the sample portion.
It could therefore be helpful to provide a method of the type set forth at the outset, by which it is possible to create conditions in pre-prepared sample portions in a laterally targeted manner and in a relatively short time, with as little damage as possible being made to the material to be examined, the conditions rendering it possible to examine a target region of interest by a method from microstructure diagnostics, in particular by transmission electron microscopy. It could further be helpful to provide a sample for microstructure diagnostics, in particular by transmission electron microscopy, the sample having an examination region suitable for examination, prepared with little damage in a predeterminable target region.